what does "2.8 spot" mean in this context?

[XINLAI-AF]

Hello,

I was wondering if somebody could take look for me at this one. what does "2.8 spot" mean in this context?

Thanks for your help.


This Professor is talking about how the asteroid belt was discovered.


Professor: Yes, I divided all those numbers by 10 by putting in a decimal point. Now I'm gonna write the names of the planets under the numbers. Mercury...Venus...Earth,,, So, what do the numbers mean?

Student: Is it the distance of the planets from the sun?

Professor: Right, in astronomical units-not perfect, but tantalizingly close. The value for Mars is off by...6 or 7 percent or so. It's...but it's within 10 percent of the average distance to Mars from the Sun. But I kind of have to skip the one after Mars for now... ... Well, this pattern is known as Bode's Law.
Um, it isn't really a scientific law, not in the sense of predicting gravitation mathematically or something, but it's attempting a pattern in the spacing of the planets, and it was noticed by Bode hundreds of years ago. Well, you can imagine that there was some interest in why the 2.8 spot in the pattern was skipped, and um.. but there wasn't anything obvious there, in the early telescopes. Then what happened in the late 1700s? The discovery of ... ?

Student: Another planet?

...

[Carlos_dfc]

Bode's Law predicts that the distances of the planets from the Sun, should go up in the following sequence (measured in Astronomical units - AU)
0.4 - 0.7 - 1.0 - 1.6 - 2.8 - 5.2 - 10.0 - 19.6 - 38.8
At roughly those distances, there are.
0.4 - Mercury - at 0.4au
0.7 - Venus - at 0.7au
1.0 - Earth - at 1.0au
1.6 - Mars - at 1.5au
2.8
5.2 - Jupiter - at 5.2au
10.0 - Saturn - at 9.5au
19.6 - Uranus - at 19.2au
38.8 - Neptune at about 30au, Pluto at about 39au

As you can see, the planets actually do occupy positions at (or very near to) those predicted by Bode's Law.
Also - you'll see that there's nothing major at 2.8au (the 2.8 'spot' in the sequence).
Or at least that's what we used to think.

We have since discovered the asteroid belt, which averages at around 2.8au - including the orbit of Ceres (discovered 1801), which is by far the most massive asteroid.

[XINLAI-AF]

[quote=Carlos_dfc;15638]Bode's Law predicts that the distances of the planets from the Sun, should go up in the following sequence (measured in Astronomical units - AU)


Hi, Carlos_dfc,

First, thank you very much, your reply is just pretty clear to me.

Then I have a question, the professor says " 2.8 spot ", what does " spot " mean? Does it mean the place, the area at the 2.8 au ?

"We have since discovered the asteroid belt, which averages at around 2.8au - including the orbit of Ceres (discovered 1801), which is by far the most massive asteroid. "

Yes, you are right. In my book, then the professor says: ...and then in 1801, the object Ceres was discovered. And Ceres was in the right place-the missing spot.
The professor says "right place", does he mean the direction, not left, or Ceres was in the correct place?

[Michael Steen]

If I may put in my two cents to Carlos's excellent reply (very very detailed!), right spot would mean correct distance from the sun. That spot would include Ceres' entire orbital path, not specifically a spot to the right or left of where it was found. As far as I can tell (and I don't have a degree in astrophysics, so take this with a grain of salt), there is no way to predict where Ceres would be found on the ecliptic until it actually was found and its orbit calculated. After that, it can be included in the catalog of orbiting bodies, and its position can be predicted.

[XINLAI-AF]

Originally Posted by Michael Steen

If I may put in my two cents to Carlos's excellent reply (very very detailed!), right spot would mean correct distance from the sun. That spot would include Ceres' entire orbital path, not specifically a spot to the right or left of where it was found. As far as I can tell (and I don't have a degree in astrophysics, so take this with a grain of salt), there is no way to predict where Ceres would be found on the ecliptic until it actually was found and its orbit calculated. After that, it can be included in the catalog of orbiting bodies, and its position can be predicted.

Thank you, Carlos and Michael !